a) Field of the Invention
The present invention relates to a stereomicroscope.
b) Description of the Prior Art
Stereoscopic microscopes which permit observing conditions of minute locations on objects in three dimensions are widely used for research, inspections, surgical operations and so on. In recent years where sophisticated techniques are prevailing in a variety of fields, it is strongly desired to obtain a stereoscopic microscope which permits observation for a long time by two persons in relaxed postures while performing works on an object from any desired directions.
As a conventional example of stereoscopic microscopes, there is known a stereoscopic microscope which was disclosed by Japanese Patent Kokai Publication No. Hei 4-156,412. This stereoscopic microscope has a composition which consists, as illustrated in FIG. 1, of an objective lens system 2, an afocal optical system 3 disposed coaxially with the objective lens system 2 and at least a pair of eyepiece optical systems 15. The stereoscopic microscope is configured so as to satisfy the desire described above by configuring the eyepiece optical systems 15 as a whole so as to be rotatable around an axis which is located in parallel with optical axes of the objective lens system 2. In FIG. 1, the reference numeral 16 represents eyes of observers and the reference numeral 17 designates optical path splitting elements disposed in the eyepiece optical systems 15.
In the case of the stereoscopic microscope illustrated in FIG. 1, however, the afocal variable magnification optical system must have a diameter of an exit pupil thereof which is large enough to cover right and left pupils for observation of the eyepiece optical systems 15. However, a stereoscopic microscope generally uses two afocal variable magnification systems. In order to enlarge a diameter of one of the two afocal variable magnification optical systems so that light bundles are incident on the two right and left eyepiece optical systems, the diameter of the exit pupil of the variable magnification optical system must be made at least double in size, whereby the afocal variable magnification optical system inevitably has a length at least two times larger than a length of each of the two afocal variable magnification optical systems. As a result, the stereoscopic microscope has a prolonged total length or a length as measured from an object to be observed to an eyepiece lens component, thereby making it rather inconvenient to perform works on and in the vicinity of a surface of the object while peeping through the eyepiece lens system.
Further, when a total length of the variable magnification optical systems is shortened without changing the enlarged diameter of the exit pupil, focal lengths of respective lens components are shortened, thereby making it difficult to manufacture the lens components with high precision in practice and adjust locations of the lens components accurately at a stage of assembly of the afocal variable magnification optical systems.
For the reason described above, it has conventionally been difficult to obtain a stereoscopic microscope comprising an objective lens system and a variable magnification optical system which are disposed on a common optical axis, and permitting performing works on a surface of an object while observing an image thereof as described above.